Paving breaker steel



June 28, 1966 c. G. IVES ETAL 3,253,295

PAVING BREAKER STEEL Filed Jan. 18, 1963 {1] [III] I1] [I11 I I um I E z T 1 2 r 2 t 2 I I I i I I 3 3 3 3 I l A TTORAIE J United States Patent land Filed Jan. 18, 1963, Ser. No. 252,383 Claims priority, application Great Britain, Mar. 30, 1962, 12,364/ 62 3 Claims. (Cl. 29994) The invention relates to paving breaker steels or borers for use with percussive drills or like tools.

Conventional paving breaker steels are formed of high carbon steel and have a shank and a shaft of hexagonal cross section, and a raised retaining collar between the shaft and the shank, the. shank in use being retained in the drill by a clip engaging the collar. The shaft is provided with a sharpened point, also usually of hexagonal section.

With the increased power of modern percussive drills these steels are found to be inefiicient, wearing and becoming blunt relatively rapidly, and since re-sharpening alters the temper of the metal, the re-sharpened point becomes blunt even more rapidly than before or breaks under the stresses set up in use. The corners of the hexagonal cross-section are also liable to damage neighbouring similar steels in storage, leading to stress raising and breaking of the damaged steel in use.

Other shapes of steel have been proposed, having short chisel or tulip heads, but although these are more efficient in use and have a greater life than conventional steels, they suffer from the disadvantage that the heads are enlarged and can become wedged behind reinforcing bars in concrete. Other proposed steels have had thickened chisel-edged heads extending nearly to the collar, with consequent excessive weight, which has made the tool unwieldy and tiring to use.

The invention provides a paving breaker steel having a shaft of circular cross-section and a head in the form of a tapered wedge, the head being of greater length than the shaft.

By a tapered wedge is here meant a form which tapers in two planes at right angles, tapering in one plane substantially to a point andv tapering to a lesser extent in the other plane, the form thus being that of a wedge of decreasing Width ending in susbtantially a chisel edge. In a preferred form of steel according to the invention the taper in the said one plane is in .two stages, the stage nearer the point being sharper than that nearer the shaft.

It has been found that such a steel is very eflicient and has a relatively long life, and the ponnt is self sharpening so that the steel can be used without re-sharpening until the greater part of the head has worn away.

The steel according to the invention has the additional advantage that since virtually the whole of the head is consumable, superfluous weight is cut to a minimum. Moreover, the round shaft contains more metal than a hexagonal shaft of the same diameter, so reducing stresses in the shaft during operation, and does not give rise to stress-raising damage when a number of steels are heaped together.

Steels according to the invention can be constructed of "ice high carbon steel of the same type as used in the manufacture of conventional breaker steels.

One embodiment of the invention is illustrated by way of example in the accompanying drawings in which FIG. 1 is a front elevation of a paving breaker steel according to the invention.

'FIG. 2 is a side elevation of the steel shown in FIG. 1.

FIG. 3 is a front elevation of a steel according to the invention having a two-stage taper.

FIG. 4 is a side elevaion of the steel shown in FIG. 3.

The steel shown in FIGS. 1 and 2 has a conventional hexagonal shank 1 for engagement in the chuck of a drill and a retaining collar 2. The shaft 3 below the collar is round, and carries the head 4 which is of rectangular cross section and tapers uniformly in two planes at right angles down to a chisel edge 5.

The steel shown in FIGS. 3 and 4 has a shank 1, collar 2 and shaft 3 of the same form as shown in FIGS. 1 and 2 but the head 4 has a two-stage taper, the taper of the upper portion 6 breaking at 7 into the more abrupt taper of the lower portion 8 down to a chisel edge 5.

Although in the. embodiment illustrated the shank above the collar is hexagonal, most percussive drills and like tools having chucks designed to take implements with hexagonal shanks, the shank may be of a cross-section other than hexagonal, and can be designed to fit the chuck of the particular drill or like tool with which it is intended to be used.

We claim:

1. A paving breaker steel comprising:

a shank;

a retaining collar formed at one end of said shank;

a shaft of circular cross-section extending from the side of said collar remote from said shank;

and a head formed integrally and coaxially with said shaft, said head having a length exceeding that of said shaft and having the form of a tapered wedge which tapers from the shaft in one plane substantially to a point and in a second plane perpendicular to said one plane to a linear terminal edge.

2. A steel according to claim 1 wherein the taper of said head in both said planes is uniform between said edge and the junction with said shaft.

3. A steel according to claim 1 wherein the taper of said head in said one plane is in two stages, the taper nearer said point being sharper than the taper nearer said shaft.

References Cited by the Examiner UNITED STATES PATENTS 1,644,110 10/ 1927 Cover et al 299-37 X 1,891,222 12/ 1932 Cornett 29994 2,161,062 6/ 1939 Killg-ore 262-40 2,302,069 11/ 194-2 Stephens 282-40 2,629,588 2/1-953 Nearnand 262-40 2,843,369 7/ 1958 Simmons 262-8 FOREIGN PATENTS 442,912 2/ 1936 Great Britain.

ERNEST R. PURSER, Primary Examiner.

BENJAMIN HERSH, CHARLES E. OCONNELL,

Examiners. 

1. A PAVING BREAKER STEEL COMPRISING: A SHANK; A RETAINING COLLAR FORMED AT ONE END OF SAID SHANK; A SHAFT OF CIRCULAR CROSS-SECTION EXTENDING FROM THE SIDE OF SAID COLLAR REMOTE FROM SAID SHANK; AND A HEAD FORMED INTEGRALLY AND COAXIALLY WITH SAID SHAFT, SAID HEAD HAVING A LENGTH EXCEEDING THAT OF 